Climate change and the Arctic Daniel J. Jacob, Harvard University Where is the Arctic sea ice today? You are here http://nsidc.org/arcticseaicenews/ The Gulf Stream keeps our sector of the Arctic warm Seasonal variation in Arctic sea ice (2014) 1970s data shown as hatched March maximum September minimum Murmansk http://nsidc.org/arcticseaicenews/ Boston Globe, July 12, 2015 Barrow, Alaska EQUILIBRIUM CLIMATE OF THE EARTH: BALANCE BETWEEN SOLAR AND TERRESTRIAL RADIATION SOLAR RADIATION (visible) 30% reflected by clouds, ice… TERRESTRIAL RADIATION (infrared) WARMING OF EARTH’S SURFACE BY GREENHOUSE GASES SOLAR RADIATION (visible) Greenhouse layer 30% reflected by clouds, ice… Greenhouse gases in atmosphere absorb infrared radiation, re-emit It both upward and downward TERRESTRIAL RADIATION (infrared) Water and CO2 are the two most important greenhouse gases CO2 is increasing because of combustion of fossil fuels Surface observations since 1958 Mauna Loa, Hawaii South Pole 9.5 billion tons of carbon per year (2011) Ice core records for past 1,000 years IPCC [2007, 2014] Global surface temperature trend over last 1,000 years IPCC [2007], GISTEMP [2015] There is large year-to-year variation on top of long-term trend February 2015 temperature anomaly relative to 1951-1980 mean; Snowmageddon in Boston Cause: meandering of the jet stream, resulting in an “Arctic vortex” GISTEMP [2015] The Arctic is warming faster than anywhere else on Earth Annual surface temperature trend, 1901-present Shrinking extent of Arctic sea ice, 1979-present summer data IPCC [2014] Melting land ice and sea level rise Sea level has risen 7 inches since 1900 land storage thermal expansion Greenland glaciers IPCC [2014] Very obvious impacts of sea-level rise Islands, low-lying areas become uninhabitable 4.9 million in US live less than 4ft above sea level Kiribati Development of the Harvard Allston campus: consideration of sea-level rise out to 2200 Future projections of CO2 emissions IPCC Representative Concentration Pathways (RCP) CO2 concentration Emission business as usual today extremely aggressive intervention What does this mean for future climate change? business-as-usual scenario: 8oF warming by 2100 extremely aggressive Intervention: climate stabilization by 2040 IPCC [2014] Projections of future sea-level rise Limiting future rise to 1 foot will require extremely aggressive intervention IPCC [2014] Eocene (55-36 million years ago): last time CO2 was above 500 ppm No ice anywhwere on Earth - crocodiles on Greenland - pine forest in Antarctica - sea level 100 m higher than today Could abrupt climate change take us back to Eocene conditions? Equilibrium climates of the Earth ENERGY positive feedback negative feedback abrupt climate change Perturbation variabilité interannuelle Stable climate 2 Stable climate 1 Stable climate 3 TEMPERATURE Temperature and CO2 in ice cores tell the story of abrupt climate change glacial glacial glacial glacial What can we do? Reduce consumption of fossil fuels: essential strategy for long term Aggressively reduce consumption of fossil fuels: energy conservation, renewable sources Present-day per capita emission of CO2 US: 5 tons per capita per year (200 lbs per week) What can we do? Climate engineering – reflecting solar radiation to space, sequestering carbon… … but we need to worry about unintended consequences!